Heaters for hot-gas engines

ABSTRACT

A heater of a hot-gas engine comprises substantially U-form tubular devices each connected between a hot chamber and a regeneration chamber of the engine. The two limbs of each device are formed by two tubes positioned one downstream of the other with respect to the flow of primary fluid medium. The limbs of the devices are transverse to this flow and are arranged side-byside in at least two rows to form at least two grids which are face-to-face with each other. The rows of limbs also extend transversely of the flow of primary medium.

[22] Filed:

United States Patent [19'] Friedemann HEATERS FOR HOT-GAS ENGINES [7 5] Inventor: Andreas Zacharias Friedemann,

Augsburg, Germany [73] Assignee: Motoren-Werke Mannheim AG Vorm, Benz ABT. Stationarer Motorenbau, Mannheim, Germany Nov. 6, 1972 21 .Appl. N0.: 304,274

[30] Foreign Application Priority Data Nov. 4, [971 Germany 2154714 [52] US. Cl 60/517, 165/176 [51] Int. Cl. F02g 1/04 [58] Fieldoi'Search 60/516-526 [56] References Cited UNITED STATES PATENTS 289,485 12/1883 .Woodbury e: a], 60/517 [451 May 7,1974

2,484,393 10/1949 Van Heeckeren 60/517 Primary Examiner-Edgar W. Geoghegan Assistant Examiner-Allen M. Ostrager Attorney, Agent, or Firm-Eric H. Waters [5 7] ABSTRACT A heater of a hot-gas engine comprises substantially U-form tubular devices each connected between a hot chamber and a regeneration chamber of the engine. The two limbs of each device are formed by two tubes positioned one downstream of the other with respect to the flow of primary fluid medium. The limbs of the devices are transverse to this flow and are arranged side-by-side in at least two rows to form at least two grids which are face-to-face with each other. The rows of limbs also extend transversely of the flow of primary medium,

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1 HEATERS FOR HOT-GAS ENGINES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a heater for a hot-gas engme.

The heater consists of a plurality of U-form tubular devices via which a secondary fluid medium, while receiving heat from a stream of primary fluid medium supplied by a heat-source, can flow from a hot chamber to a cold chamber of the hot-gas engine by way of a regeneration chamber and a cooler, as well as in the reverse sense, the two limbs of each U-form device being positioned one downstream of the other in the path of flow of the primary medium, one limb being connected to the hot chamber and the other limb to the regeneration chamber.

The heater is the heat-exchanger on the energy input side of the hot-gas engine and performs the function of picking up heat from the stream of primary medium, e.g., combustion gas, while cooling this stream, and of passing the heat to the circulating secondary medium,

e.g., helium. In this system, the energy represented by the temperature difference between the two media must be utilized as completely as possible. On the other hand, the heater should be of limited size, since the space for the secondary medium constitutes a dead space for the hot-gas engine.

2. Description of the Prior Art A heater, likewise consisting of tubular devices, is illustrated and described in German Patent Specification No. 806,740, for example. It fulfils the requirements mentioned in the preceding paragraph only by means of a construction which is difficult to produce and is trouble-prone in operation. In this known heater, the U-form tubular devices are disposed at the periphery of a cylindrical combustion chamber, one end face of which is constituted by the heat-source in the form of a burner, while its other end face is formed by the wall of the hot chamber. The combustion gases first flow in an axial direction of the combustion chamber and are diverted towards the tubular devices on the wall of the hot chamber. For this diversion it is necessary to use a heat shield, but the latter is not strong enough to resist the effect of the combustiori gases, the temperature of which may be as high-as 2,000C. A further disadvantage of the known construction resides in the fact that each of the cylinders of a multi-cylinder hot-gas engine which are arranged in line has to be equipped with its own burner and all the associated ancillary means such as air pre-heaters and fuel atomizers.

SUMMARY OF THE INVENTION.

According to the present invention, there is provided a heater for a hot-gas engine, comprising a plurality of substantially U-form tubular means each for connection at one end to a hot chamber and at the other end to a regeneration chamber to conduct a secondary fluid each other, and said rows also extending transversely of said path.

By arranging the tubular means, i.e., tubular devices in this way, the need to deflect the stream of primary medium by an uncooled component such as a heat shield can be avoided. Since deflection need not take place, a blower for combustion. air will have less resistance to overcome and therefore less power is required for driving it. Considerably greater freedom of choice is offered as regards the arrangement of the burner or burners in relation to the working cylinders of the hotgas engine; for example several working cylinders of an in-line engine may be served by a single burner. In contrast to the-conditions existing in the case of the known arrangement of the tubular devices in a circle, thermal expansion in the tubular devices under the effect of the primary medium flowing through the heater and'of the associated higher temperature on the approach side can take place freely. In the known arrangement, the bends curve outwardly towards the stream of primary medium, whereas the system of grids in accordance with the invention no longer gives changes in the crosssections of the gaps between the limbs for the stream of primary medium. These cross-sections should be maintained in a precise manner and should remain unchanged during operation, since their size determines the quantity of heat extracted from the stream of primary medium.

Advantageously, heat-transfer capacities of substantially equal magnitude are achieved for all the limbs involved by providing all the limbs, or only those disposed downstream of the first grid, with heat-transfer fins, the surfaces of the fins on each grid first approached being smaller than those of the subsequently approached grids. The result of this isthat, in a twogrid as well as in a four-grid arrangement, the same proportion of the energy potential available from the stream of primary medium is transferred in each grid to the secondary circuit. In the case of a three-grid arrangement, in which the second and third grids each comprise only half as many limbs as does the first grid,

- just as much heat is transferred by the first tube grid as by the two following grids.

Greater freedom of choice in the arrangement of the fins is advantageously achieved by the use of three grids, the arrangement of the tubular devices being such that tubular devices the limbs of which are disposed in the first and second grids alternate with tubular devices the limbs of which are disposed in the first and third grids, the primary medium flowing successively through the first, second and third grids. In this arrangement, the secondary medium first flows through the first grid, which may have no tins, and then through the second or third grid,-the second grid being provided with relatively small fins and the third grid with relatively large wide fins. The outlet ends of the second and common collector, and then through the third and fourth grids, the outlet ends of which are connected to a collector. With this arrangement, the height and/or width of the heater can be reduced as compared with the arrangement comprising two grids. For a like height of grid, the four-grid heater can be approximately 30 40 percent smaller in width than the two-grid heater, since correspondingly fewer limbs can be contained in each grid. When the width is the same, the four-grid heater can be approximately percent lower in height than a two-grid heater. The volume of the structure of the hot-gas engine is decisively reduced by the reduction in the approach surface of the heater. In the four-grid heater the gaps among the limbs are considerably greater than in the case of the two-grid heater. Thus, no problem arises in fitting the heaters and the associated collectors side-by-side in the case of a multicylinder in-line engine.

As already mentioned, the U-form tubular devices are connected at the free ends of their limbs to collectors which for reasons of manufacture may be advantageou sly formed integrally with the walls of the hot chamber or the regeneration chamber. However, they may instead simply be connected to the walls of these chambers.

To improve the transfer of heat from the stream of primary medium to the fins, the surfaces of the fins may be advantageously dimpled or otherwise roughened to increase turbulence of flow.

Each U-form tubular device can be produced in an economical and advantageous manner by being composed of two straight tubes and a bend. Such separate parts are suitable for meeting the requirements of a high-quality casting process, particularly as regards the manufacture and mounting of the mould core. The use of a high-quality casting process enables those heatresisting materials to be employed which are not capable of being shaped by a plastic-shaping operation or by machining. It thus becomes possible to increase the working temperature or pressure of the hot-gas engine while obtaining the same service life from the components of the heater, and thus to increase the power density.

The U-form tubular devices can also be constituted by drawn tubes in heat-resisting wrought alloys, any heat-transfer fins that are required being attached to the tubes by soldering. In this way bending and manipulating of the tubes and thus local excess stretching which may lead to cracks are avoided. The use of straight tubular limbs reduces the number of operations during manufacture. To ensure that the flow of heat from the fins to the limbs is as uniform as possible, the fins may be advantageously'shorter on the upstream side than on the downstream side.

In multi-cylinder engines, a common duct for the primary medium and a common unit for preheating the air, which result in a simple construction, can be achieved by accommodating the heaters of the individual cylinders side-by'side in a single duct for the primary medium.

In order to even out the thermal loading of the heaters, a plurality of burner chambers may be expediently provided in the duct for the primary medium.

The control of combustion is, however, rendered considerably less complicated if only one burner chamber, common to all the cylinders, is provided in the duct for the primary medium.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be clearly understood and readily carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

FIG. 1 shows a section through a U-form tubular device of a two-grid heater of a hot-gas engine, the section being taken on the lines I-l of FIG. 3,.

FIG. 2 is a front elevation of the heater,

FIG. 3 is a plan view of the heater,

FIG. 4 is a partial section through two U-fonn tubular devices of a three-grid heater of a hot-gas engine, the section being taken on the lines IV-IV of FIG. 5,

FIG. 5 is a plan view of the three-grid heater,

FIG. 6 is a partial section through two U-fonn tubular devices of a four-grid heater of a hot-gas engine, the section being taken on the line VIVI of FIG. 7,

FIG. 7 is a plan view of the four-grid heater,

FIG. 8 shows a partial section through part of the hot gas engine including the two-grid heater of FIGS. 1 to FIG. 9 is a plan view of the part illust-ratedin FIG. 8,

FIG. 10 shows a front elevation of the part illustrated in FIG. 8,

FIG. 11 shows a partial section through part of the hot-gas engine including the three-grid heater of FIGS. 4 and 5,

FIG. 12 is a section through the hot-gas engine shown partly in FIGS. 8 to 10, and

FIG. 13 is a plan view of the hot-gas engine of FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The main component of the two-grid heater which is illustrated in FIGS. 1, 2 and 3, is a U-form tubular device l which consists of a plain tube 2, a tube 4 having large narrow heat transfer fins 3 and a bend 5. In a modification of the version illustrated, the tube 2 may have small heat-transfer fins. In the three-grid form of heater illustrated in FIGS. 4 and 5, two types of U-form tubular devices 6 and 10 are present. Each device 6 consists of a plain tube 2, a short bend 7 and a tube 8 having small circular heat-transfer fins 9. Each device 10 consists of a plain tube 2, a medium sized bend 11 and a tube 13 provided with large wide heat-transfer fins 12. In the case of the four-grid heater illustrated in FIGS. 6 and 7, two types of U-form tubular devices 14 and 18 are likewise present. Each device 14 consists of a plain tube 2, a large bend 15 and a tube 17 provided with large narrow heat-transfer fins 16 offset with respect to the axis of the tube 17 in the direction of flow A of the primary medium. Each device 18 consists of a tube 8 fitted with small circular heat-transfer fins 9, a short flat bend l9 and a tube 21 provided with medium-sized circular heat-transfer fins 20. The tubes 2 and 4, 2 and 8, 2 and 13, 2 and 17, or 8 and 21, form the limbs of a U, the connecting web of the U being constituted by the bend 5, 7, 11, 15 or 19. In each version of heater illustrated in FIGS. 1 to 7, the limbs 2, 4, 8, 13, 17 or 21, are arranged side-by-side in a row to form flat grids. The hot primary medium flows in the direction A at right-angles to the planes of the grids, as well as at right angles to the axes of the limbs 2, 4, 8, 13, 17 and 21. The planes of the grids are indicated by the numerals 22 and 23 (FIG. 3) in the case of the two-grid heater. In the three-grid heater illustreated in FIGS. 4 and 5, the plane of the first grid is designated by the numeral 22, that of illustrated second grid by the numeral 23 and that of the third grid by. the numeral 24. In the four-grid heater illustrated in FIGS. 6 and 7, the plane of the first grid is designated by the numeral 22, that of the second grid by the numeral 23, that of the third grid by the numeral 24 and that of the fourth grid by the numeral 25 (FIG. 7). In the two-gridheater illustrated in FIGS. 1, 2 and 3, the free ends of the limbs 2 and 4 are connected to collectors 26 and 27 (FIGS. 1, 2, 8, 9 and 10). The collector 26 extends to the hot chamber 28 and the collector 27 to the regeneration chamber 29. In the three-grid heater illustrated in FIGS. 4 and 5, the free ends of the limbs 8 and 9 as illustrated in FIG. 11, are connected to a double collecmi 30 which leads to the regeneration chamber 29. The free ends of the limbs 2, as in the two-grid heater, are connected to a single collector 26 which leads to the hot chamber 28. In the four-grid heater illustrated in FIGS. 6 and 7, the limbs 2 and 8 are connected to a double collector 31 which leads to the hot chamber 28. As in the case of the three-grid heater the limbs 17 and 21 are connected to the regeneration chamber 29 through a double collector 30. The collectors 26, 27, 30 and 31 are integral with the walls of the chambers 28 and 29 as seen in FIGS. 1, 2, 6, 8, 9, l0, l1 and 12. However, they may instead simply be connected to these walls. The tubes 2, 4, 8, 13, 17 and 21 are connected to the bends 5, 7, 11, and 19 and to the collectors 26, 27, 30 and 31 by a high-temperature vacuum soldering process. The heat-transfer fins 3, 9, 12, 16 and can be made integral with thetubes 2, 4, 8, 13, 17 and 21, a high-quality casting process being employed for the purposerl-Iowever, the fins may instead be soldered on to these tubes, which in this case are drawn tubes of heat-resisting wrought alloys. For the purpose of improving heat transfer the surfaces of the heat-transfer fins 3, 9, 12, 16 and 20 maybe dimpled or otherwise roughened. As shown in FIG. 6 in the case of the finsl6, the fins may be shorter on the upstream side of the tubes 17 than on the downstream side, in order to ensure the greatest possible uniformity in the flow of heat to the tubes 17. In theembodiments illustrated in FIGS. 12 and 13, the hot primary medium is supplied by one or more burner chambers 32 to which the combustion air is supplied by a blower, not illustrated, by way of an inlet orifice 33 and an air preheater 34, as indicated by the arrows. After the gaseous products of combustion have yielded most of their heat via the devices 1, 6, l0, l4 and 18 to the secondary means circulating through the devices 1, 6, 10, 14 and 18, and have warmed with combustion air in the preheater 34, these products issue from an orifice 35. The heaters of the cylinders of the hot-gas engine, in which the cylinders are arranged in line, can be arranged side-by-side in a single duct 36 for the primary medium, as shown in FIG. 13. As shown in this Figure, a plurality of burner chambers 32 can be provided in the duct 36. However, it is possible to provide only one burner chamber 32 for each duct 36 common to a plurality of cylinders. The devices 1, 6, 10, 14 and 18 can be arranged in any desired positions with respect to the axis 37 of the engine above the hot chambers 28 and the regeneration chambers 29, depending upon the space conditions. It is possible to construct single-cylinder and multi-cylinder hot-gas engines and double-acting hot-gas engines with the aid of identical units formed by the walls of the hot chamber 28 and the regeneration chamber 29, the collectors 26 and 27, or 26 and 30, or 30 and 31, which constitute heat-resisting components, together with one of the types of heater described. The planes 22, 23, 24 and 25 of the grids do not need to be absolutely flat. They may also be slightly curved provided that the thermal expansion of the devices 1, 6, 10, 14 and 18 does not cause any harmful change in the-gaps between the limbs 2, 4, 8, 13, 17 and 21 or between the heat-transfer fins 3, 9, 12, 16 and 20. The bends 5, 7, 11, 15 and 19 do not need to be separate parts as illustrated in FIGS. 2, 3, 5 and 7. As shown in FIGS. 9 and 10 they may also be formed in one piece for each grid.

I claim:

1. In a hot gas engine, a'combination comprising a heater, means for supplying a hot primary fluid medium to said heater, a hot chamber connected to said heater for supplying thereto a secondary fluid medium to be heated in said heater, and a regeneration chamber connected to said heater to receive said secondary fluid medium therefrom, said heater comprising a plurality of substantially U-form tubular means each connected at one end to said hot chamber and at the other end to said regeneration chamber, the two limbs of each U- forrn tubular means being positioned one downstream of the other with respectto the intended path of flow of said primary fluid medium through the heater, the limbs of the U-form tubular means extending transversely of said path and being arranged side-by-side in at least two rows to form at least two grids arranged face-to-face with respect to each other, and said rows also extending transversely of said path.

2. A combination according to claim 1, and further comprising heat-transfer fins provided on the limbs of the or each grid downstream of the first grid in said path.

3. A combination according to claim 2, wherein said fins are roughened for the purpose of increasing turbulence of flow of said primary fluid medium.

4. A combination according to claim 2, wherein each fin projects further downstream from the associated limb than it projects upstream from the limb.

5. A combination according to claim 2, wherein said grids are at least three in number and the areas of, the fins provided on the second grid in said path are smaller than the areas of the fins provided on the or each grid downstream of said second grid.

6. A combination according to claim 1, wherein said grids are three in number, some of the U-form tubular means having their limbs in the first and second grids in said path and alternating with the remaining U-form tubular means, which have their limbs in the first and third grids in said path.

7. A combination according to claim 1, wherein said grids are four in number, some of the U-form tubular means having their limbs in the first and fourth grids in said path, and being disposed adjacent to respective ones of the remaining U-form tubular means, which have their limbs in the second and third grids in said path.

8. A combination according to claim 1, and further comprising collectors which are integral with respective walls of said hot chamber and said regeneration chamber and via which said tubular means are connected to said hot chamber and said regeneration chamber.

9. A combination according to claim 1, wherein each tubular means comprises two co-extensive straight dium therefrom, each heater comprising a plurality of substantially U-form tubular means each connected at one end to said hot chamber and at the other end to said regeneration chamber, the two limbs of each U- form tubular means being positioned one downstream of the other with respect to the intended path of flow of said primary fluid medium through the heater, the limbs of the U-form tubular means of each heater extending transversely of said path and being arranged side-by-side in at least two rows to form at least two grids arranged face-to-face with respect to each other, and said rows also extending transversely of said path.

12. A combination according to claim 11, wherein said means for supplying said primary fluid medium comprises a plurality of burner chambers.

* III 

1. In a hot gas engine, a combination comprising a heater, means for supplying a hot primary fluid medium to said heater, a hot chamber connected to said heater for supplying thereto a secondary fluid medium to be heated in said heater, and a regeneration chamber connected to said heater to receive said secondary fluid medium therefrom, said heater comprising a plurality of substantially U-form tubular means each connected at one end to said hot chamber and at the other end to said regeneration chamber, the two limbs of each U-form tubular means being positioned one downstream of the other with respect to the intended path of flow of said primary fluid medium through the heater, the limbs of the U-form tubular means extending transversely of said path and being arranged side-by-side in at least two rows to form at least two grids arranged face-to-face with respect to each other, and said rows also extending transversely of said path.
 2. A combination according to claim 1, and further comprising heat-transfer fins provided on the limbs of tHe or each grid downstream of the first grid in said path.
 3. A combination according to claim 2, wherein said fins are roughened for the purpose of increasing turbulence of flow of said primary fluid medium.
 4. A combination according to claim 2, wherein each fin projects further downstream from the associated limb than it projects upstream from the limb.
 5. A combination according to claim 2, wherein said grids are at least three in number and the areas of the fins provided on the second grid in said path are smaller than the areas of the fins provided on the or each grid downstream of said second grid.
 6. A combination according to claim 1, wherein said grids are three in number, some of the U-form tubular means having their limbs in the first and second grids in said path and alternating with the remaining U-form tubular means, which have their limbs in the first and third grids in said path.
 7. A combination according to claim 1, wherein said grids are four in number, some of the U-form tubular means having their limbs in the first and fourth grids in said path, and being disposed adjacent to respective ones of the remaining U-form tubular means, which have their limbs in the second and third grids in said path.
 8. A combination according to claim 1, and further comprising collectors which are integral with respective walls of said hot chamber and said regeneration chamber and via which said tubular means are connected to said hot chamber and said regeneration chamber.
 9. A combination according to claim 1, wherein each tubular means comprises two co-extensive straight tubes and a tubular bend interconnecting adjacent ends of these tubes.
 10. A combination according to claim 1, wherein each tube is a drawn tube of a heat-resisting wrought alloy.
 11. In a hot-gas engine, a combination comprising in-line cylinders, heaters associated with the respective cylinders, means for supplying a hot primary fluid medium to said heaters, hot chambers of said cylinders connected to the respective heaters for supplying thereto a secondary fluid medium to be heated in said heaters, and regeneration chambers connected to the respective heaters to receive said secondary fluid medium therefrom, each heater comprising a plurality of substantially U-form tubular means each connected at one end to said hot chamber and at the other end to said regeneration chamber, the two limbs of each U-form tubular means being positioned one downstream of the other with respect to the intended path of flow of said primary fluid medium through the heater, the limbs of the U-form tubular means of each heater extending transversely of said path and being arranged side-by-side in at least two rows to form at least two grids arranged face-to-face with respect to each other, and said rows also extending transversely of said path.
 12. A combination according to claim 11, wherein said means for supplying said primary fluid medium comprises a plurality of burner chambers. 